Variable inductor



' Aug. 9, 1966 R. H, OLSON VARIABLE INDUGTOR 2 Sheets-Sheet 1 Filed Oct. 7, 1964 WWI/V7314 fay/41 0.4 JO/V, EM 9% h m 1966 R. H. OLSON 3,265,9Q7 VARIABLE INDUCTOR 2 Sheets-Sheet 2 Filed Oct. 7, 1964 WAC/V701 foyA! 0.4 50%, By

+ QMN 9% United States Patent 3,265,997 VARIABLE INDUCTOR Roy H. Olson, Palos Verdes Estates, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Oct. 7,1964, Ser. No. 402,217 4 Claims. (Cl. 333-73) This invention relates to a variable inductor for highpower applications and, more particularly, to an apparatus capable of providing a variable inductance with no moving or sliding contacts.

In order to provide a high-power transmitter capable of being tuned over a broad range of frequencies, it is generally necessary to be able to vary the inductance as well as the capacitance in the tank circuit of the output stage. It has been found that when moving or slidingcontacts are employed to short out varying portions of a coil, arcing and overheating often result. Also, shorted out sections of the coil may form resonant circuits which generate spurious frequency signals that are detrimental to the efficient operation of the transmitter.

It is therefore an object of the present invention to provide an improve variable induct-or for use in high power radio frequency applications.

Another object of the present invention is to provide a variable inductor that does not employ moving or sliding contacts to short out portions of a coil to vary th inductance thereof.

Still another object of the invention is to provide an inductor that can be varied an unlimited number of times without wear occurring at the radio frequency surfaces.

In accordance with the present invention, a conductive coil of uniform diameter is provided. In the usual case, the coil itself may be constructed sufficiently rigid as to not require any additional support. In situations where this is not the case, dielectric support may be provided on the outer portion of the coil. 'In addition, a conductive slidably mounted rotatable cylinder is mounted axially within the coil and an edge-wound conductive helix of a pitch equal to that of the coil attached to the outer surface thereof. The edge-wound helix of this assembly is maintained at a fixed reference so as to center the respective turns of the coil between the successive turns of the helix whereby rotation of the cylinder causes the degree to which the coil is enveloped by the edge-wound helix and cylinder to change. The edge-wound helix and cylinder together with the portion of coil enveloped form an open-sided electro-magnetic wave transmission circuit. An appropriate transition is provided at one extremity of-the coil to a coaxial line which utilizes an extension of the conductor forming the coil as the center conductor thereof.

In operation, the coil remains fixed and the turns of the coil not enveloped by the cylinder and edge-wound helix assembly provide the variable inductor. Rotation of the cylinder either increases or decreases the number of turnsenveloped thereby varying thhe inductance of the coil. The portion of the coil enveloped by the cylinder and edge-wound helix assembly provides the center conductor of the open-sided waveguiding apparatus which presents a constant low-loss impedance in series with the coil. 7

The above-mentioned and other features and objects of this invention and the manner of obtaining them will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a side elevation view of the apparatus of the present invention;

Patented August 9, 1 966 FIG. 2 shows cross-section 2-2 of the-apparatus of FIG. 1; and

FIG. 3 shows the cross-section 3-3 of the apparatus of FIG. 2. 1

Referring now to FIG. 1 of the drawings, there is shown a side-elevation perspective view of a preferred embodiment of the variable inductor of the present invention. In particular, the variable inductor of the present invention comprises a rigid coil 10 of constant pitch and diameter. Rigid coil 10 has an input conductor 11 and an output conductor 12 which are extensions of the same material which forms the coil 10. The input and output conductors 11, 12 extend through an insulative deck 14 and are fastened on the opposite side thereof by conventional means, not illustrated, thereby maintaining the coil 10 in a fixed position relative to deck 14.

A square bar 15 is mounted coaxially through the rigid coil 10' and is adapted to be rotated by means of a mechanical coupling 16 to a motor 17. In addition, aconductive cylinder 18 of a length comparable to that of rigid coil 10 and having an outer diameter substantially equal to the inside diameter less the pitch of rigid coil 10 is slidably mounted coaxially about square bar 15 by means of spiders 19, 20. Thus, conductive cylinder 18 will rotate with square bar 15 and will slide freely therea-long. A conductive edge-wound helix 21 ofwidth of from one and one-half to two times the pitch of rigid coil 10, a pitch equal to that of rigid coil 10 and having an inside diameter equal to the outside diameter of cylinder 18 is disposed circumferentially about and in electrical contact with said cylinder coextensive with the length thereof. A support element 22 is afiixed to the deck 14 and includes wiping contacts 23, 24 which maintain the respective turns of edge-wound helix 21 spaced symmetrically between the turns of rigid coil 10.

Referring now to FIG. 2 of the drawings, there is illustrated the cross-section 22 of FIG. 1 showing details of the transition apparatus 25 connecting the opensided coaxial conductor assembly formed by the rigid coil 10, edge-wound helix 21 and cylinder 18 to an output coaxial conductor 26. Transition apparatus 25 includes conductive side elements 27, 28 (see FIG. 1) disposed sy-mmetrically about the output conductor 12 of coil 10 and conforming to but not touching the outer configuration of adjacent turns of the edge-wound helix 21. Conductive sheets 29, 31) disposed substantially parallel to the output conductor 12 and extending from the outer configuration of edge-wound helix 21 to the deck 14 connect the side elements 27, 28. A flange 31 secures the side elements 27, 28 and sheets 29, 30 to the deck 14. Output coaxial conductor 26 is connected to the transition apparatus 25 by conventional means and may additionally provide a transition to coaxial line of circular cross-section, if desired. Lastly, a lead 32 connects the wiping finger contacts 23, 24 to the transition apparatus 25 to provide continuity in the propagation of energy from the coil 10.

Referring to FIG. 3, there is shown the cross-section 33 of FIG. 2 to illustrate the location of the turns of rigid coil 10 relative to the edge-Wound helix 21 and cylinder 18. Designating the distance between successive turns of the edge-wound helix 21 as P, the center of the turns of rigid coil 10 is disposed the distance P/ 2 from the helix 21 and outer surface of cylinder 18. Further, the width of the edge-wound helix 21, although not critical, is preferably made no less than 3P/ 2 to avoid mutual coupling between the turns of rigid coil 10 enveloped by the helix 21 and cylinder 18 assembly. The actual cross-sectional diameter of the turns of coil 10 relative to the dimension P determines the impedance of the transmission line thus formed; i.e., the nearer the of turns of rigid coil necessary to achieve a selectedinductance. The turns of coil 10, irrespective of the number, are converted into transmission line which presents a constant impedance at the termination of the active turns of coil 10. The electrical connection provided by lead 32 provides for continuity of the wave when leaving the edge-wound helix 21 to the transition apparatus 25.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those slsilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

What is claimed is:

1. A variable inductor comprising a rigid conductive coil of unifiorm pitch and radius, said coil having input and output conductors; means for enveloping determinable portions of the turns of said rigid coil on two sides between successive turns thereof and on no less than one of the inner and outer sides of the turns thereof by a conductive material thereby to convert said determinable portions into a helical transmission line of substantially constant impedance whereby the remaining portions of 'said coil'p-rovide a selected inductance; and means disposed about said output conductor and juxtaposed to at least a portion of said conductive material adjacent thereto thereby to provide a stationary transmission line output form said variable inductor.

2. The variable inductor as defined in claim 1 wherein only said inner side of said inner and outer sides of said determinable portions of the turns of said rigid coil are enveloped by said conductive material whereby said helical transmission line is open-sided.

3. A variable inductor comprising a rigid conductive coil of uniform pitch and radius, said coil having input and output conductors; a conductive cylinder of a diameter substantially equal to the inner diameter minus the pitch of said coil and of a length comparable to the' length of said coil disposed coaxially rotatable about and slidably along the center axis of said coil; a conductive edge-wound helix of an inner diameter equal to the diameter of said cylinder, of a pitch equal to said uniform pitch of said coil and of a width no less than one and one-half times said uniform pitch disposed about and in electrical contact with said cylinder coextensive with the length thereof; means slidably connected to said edge- Wound helix for maintaining the turns thereof midway between turns of said rigid coil; means coupled to said cylinder for rotating said cylinder and edge-wound helix thereby to convert determinable portions of said rigid coil into transmission line; and means disposed about said output conductor and juxtaposed to the portions of said edge-wound helix adjacent thereto for providing a stationary output transmission line.

4. The variable inductor as defined in claim 3 wherein said edge-wound helix and said cylinder are electrically connected to said means for providing an output transmission line.

No references cited.

LEWIS H. MYERS, Primary Examiner. 

1. A VARIABLE INDUCTOR COMPRISING A RIGID CONDUCTIVE COIL OF UNIFORM PITCH AND RADIUS, SAID COIL HAVING INPUT AND OUTPUT CONDUCTORS; MEANS FOR ENVELOPING DETERMINABLE PORTIONS OF THE TURNS OF SAID RIGID COIL ON TWO SIDES BETWEEN SUCCESSIVE TURNS THEREOF AND ON NO LESS THAN ONE OF THE INNER AND OUTER SIDES OF THE TURNS THEREOF BY A CONDUCTIVE MATERIAL THEREBY TO CONVERT SAID DETERMINABLE PORTIONS INTO A HELICAL TRANSMISSION LINE OF SUBSTANTIALLY CONSTANT IMPEDANCE WHEREBY THE REMAINING PORTIONS OF SAID COIL PROVIDE A SELECTED INDUCTANCE; AND MEANS DISPOSED ABOUT SAID OUTPUT CONDUCTOR AND JUXTAPOSED TO AT 